1. Field of the Invention
The present invention related to an electron beam exposure apparatus. In particular, the present invention relates to an electron beam exposure apparatus, in which generation of contamination inside the apparatus can be suppressed, and to a method for cleaning the electron beam exposure apparatus.
2. Description of the Prior Art
In processes of manufacturing a semiconductor device, an electron beam exposure apparatus capable of exposing a fine pattern is used. In a recent electron beam exposure apparatus, in order to improve throughput, there is used a mask that has a slit or a group of various kinds of opening patterns, for forming various shapes of cross-sections of beam. Then, the electron beam passed through these masks is irradiated onto a surface of a sample.
When exposure is carried out with such an electron beam exposure apparatus, the position of irradiating the electron beam changes with elapse of time. Consequently, the change leads to a phenomenon that an exposure pattern is deteriorated. Such displacement of irradiation position of the electron beam is referred to as beam drift. It is considered that the beam drift is caused as follows.
When an electron beam is irradiated onto a resist film applied to a surface of a sample, an organic material forming the resist film generates a gas.
Carbon components contained in the generated gas adhere onto a surface of each part inside the exposure apparatus to form contamination. In addition, the vacuumed exposure apparatus contains hydrocarbon (CxHx) therein, and this hydrocarbon also forms contamination. When electric charges are accumulated on this contamination, an electric field is generated by a difference of the amounts of accumulated electric charges. This electric field deflects the electron beam to be irradiated. As a result, the irradiation position of the electron beam varies.
For such a problem, there have been proposed various methods for reducing the generation of contamination inside the electron beam exposure apparatus.
As a technique with regard to this, Japanese Patent Application Laid-open Publication No. 09-259811 discloses a method for cleaning the inside of a chamber by using ozone in an electron beam exposure apparatus.
In the above-described method for preventing the generation of contamination inside the chamber, the generation of contamination is prevented by injecting ozone into the apparatus with the apparatus being operated. In other words, ozone is caused to collide with an electron beam inside the apparatus to be decomposed into oxygen and active oxygen. After that, the active oxygen generated through the decomposition reacts with the contamination which would otherwise adhere to the sample and the surface of each part inside the apparatus, and then evaporates the reaction product as a carbon monoxide gas.
However, it was observed that even if the inside of the exposure apparatus was cleaned by the above-described cleaning method, beam drift was still generated.
As described above, the reason for causing the beam drift is that electric charges are accumulated on the contamination, and an electric field is generated. On the other hand, the reason for causing the beam drift even after the contamination is removed is that an insulator, which is different from the contamination, is generated by injecting an ozone gas into the chamber.
The insulator includes SiO2, which is formed, for example, due to oxidation, by the ozone gas, of silicon constituting a mask for forming an electron beam.
As a countermeasure against this problem, it is also possible that a metal, which does not become an insulator even after being oxidized, such as titanium, is attached to the surface of the mask. However, in this case, an oxide of the attached metal is formed which causes deformation of the mask per se. As a result, it becomes difficult to accurately carry out the exposure process.